Incising the skin is likely to introduce Propionibacterium into the surgical field

These authors studied 50 patients undergoing open shoulder surgery after receiving 2 g intravenous cefazolin 30 minutes before the skin incision. A wide range of shoulder surgeries were included, ranging from Latarjet to reverse total shoulder to AC joint reconstruction to fracture fixation.

The first swab was termed ‘‘pre-prep.’’ This was taken from the skin surface over the intended incision site, after administration of intravenous antibiotics but before skin preparation with ChloraPrep.

The skin was then prepared with 70% alcoholic chlorhexidine.

The second swab was termed ‘‘post-prep.’’ This was taken from the skin surface over the intended incision site, after skin preparation with ChloraPrep once it was dry.

The third swab was termed ‘‘dermal swab.’’ This was taken from the exposed dermal surface within the wound immediately after the skin had been incised.

A tissue biopsy specimen was termed ‘‘dermal biopsy.’’ This was a 3-mm to 5-mm specimen taken from the dermis within the wound using a fresh blade, skin hooks, and forceps were used to harvest the specimen.

Anaerobic cultures were observed for a minimum of 14 days. Colonies were identified as P acnes by matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry.
P acnes was cultured in 21 of 50 prepreparation skin surface swabs (42%), 7 of 50 postpreparation skin surface swabs (14%), 26 of 50 dermal swabs (52%), and 20 of 50 dermal biopsy specimens (40%). Twelve swabs were positive for an organism other than P acnes . In the pre-prep swabs, 8 Staphylococcus epidermidis , 1 S capitis , and 2 S aureus were cultured. S capitis was also cultured in a dermal swab in a patient who was positive for P acnes.

No difference was found in the incidence of P acnes according to the surgical approach (deltopectoral, posterior, superior, or deltoid split) performed.

There was a significantly higher incidence of P acnes growth from the skin surface (P = .009) and dermis (P = .01) of patients aged ≤50 years old and a trend toward increased incidence of P acnes in men.

P acnes growth from a prepreparation skin surface swab had a sensitivity of 69%, specificity of 88%, positive predictive value of 86%, and negative predictive value of 72% at predicting subsequent P acnes growth from the dermal swab or biopsy specimen.

Taken together, these findings suggest that the dermis is often not sterilized by common antibiotics and surgical preparation and that the bacteria in the opened sebaceous glands can inoculate the wound after skin incision, injection, or arthroscopic surgery.

These data suggest that preoperative epidermal skin swabs may be a way to identify individuals at higher risk for Propionibacterium infection.